Lateral-flow or immunochromatographic test kits and methods for the detection of the presence or concentration of chemical residues or analytes or classes thereof from liquid samples have been developed. An example of one such test kit includes a pregnancy test kit, for example, U.S. Pat. No. 5,266,497. Similar devices are used for chemical residue detection utilizing an enzyme conjugate, for example, U.S. Pat. No. 4,999,285. For antibiotics, IDEXX has been using a two element-assay including a test tube (containing enzyme-conjugate receptor) and a lateral-flow device (containing immobilized analyte). This device has been commercially marketed as the SNAP test. In addition, competition assays for drugs in urine and serum have been described using 0.1–1 μm color beads with sensitivity levels of 300 ppb (Sun et al. U.S. Pat. No. 5,238,652). All these assays have the drawback that they are overly sensitive for some residues which has the potential to result in a sample testing positive that is actually acceptable by the regulations as negative. The current invention will correct this problem, while simplifying the test and making it more acceptable as a screening test to regulatory, industry, and consumer entities.
Particularly in the food safety area, it has long been recognized that residue detection should be accurate, inexpensive and easily conducted. Consumers and governments are becoming increasingly aware of the necessity for testing foods for the presence of undesirable residues naturally occurring or otherwise.
Since a large portion of the consumers are children, food safety has long been critical in the dairy industry. Antibiotic residues used on a dairy farm occasionally appear in the milk supply. The hazards associated with these undesirable residues include: allergic reactions, assisting the propagation of new and sometimes drug-resistant microorganisms and other long term health risks.
Government agencies have established, in some cases, legal limits for particular-residues in foods, for example, antibiotic residues in milk. Residues above the “legal” limit are considered unsafe for human consumption. Residue levels below the legal limit are considered “safe”. It is important, therefore, that detection methods, in addition to being inexpensive and easily conducted, do not give positive results when residues are below legal limits, so that otherwise acceptable milk, or other foods, are not discarded or otherwise treated as containing residues above legal limits.